1. Field of the Invention
The present invention is related to a reflection type display apparatus for displaying characters and the like by reflecting light entered from a front surface thereof and then controlling this reflection light by every pixel, and also related to a method of manufacturing such a reflection type display apparatus, and an electronic appliance using this reflection type display apparatus.
2. Description of the Related Art
Display apparatus such as liquid crystal display apparatus are mainly subdivided into transmission type display apparatus and reflection type display apparatus. As to a transmission type liquid crystal display apparatus, since a liquid crystal display panel is illuminated by a back light mounted on a rear surface thereof, a display screen becomes bright. However, since the back light must be continuously turned ON while the transmission type liquid crystal display apparatus is used, high power consumption thereof is required. As a result, reflection type liquid crystal display apparatus are preferably employed in portable appliances using batteries, for example, portable telephones.
In a reflection type liquid display apparatus, while a reflection plane is provided on a rear surface of a liquid crystal layer, since a display screen of this reflection type liquid crystal apparatus is illuminated, or lightened in such a manner that external light (namely, light such as directly-entered sunlight and lightening light, which is entered from peripheral portion) which is entered into the display screen of this display apparatus is reflected on the reflection plane under bright peripheral environment, power consumption thereof may be suppressed. Such reflection type liquid crystal display apparatus are further subdivided into a semi-transmission type liquid crystal display apparatus and a full (total) reflection type liquid crystal display apparatus.
A semi-transmission type reflection-mode liquid crystal display apparatus is arranged in such a manner that a large number of very small windows are opened in a reflection plane, and a back light is arranged behind the reflection plane. When the back light is turned ON, since a display screen is lightened by light of the back light, which has passed through very small windows (through holes), a display content of this semi-transmission type reflection-mode liquid crystal display apparatus may be recognized even in a dark place. However, since a large number of windows are opened in the reflection plane in such a semi-transmission type reflection mode liquid crystal display apparatus, an optical reflection efficiency (reflectance factor) at this reflection plane is lowered. As a result, when the semi-transmission type reflection-mode liquid crystal display apparatus is used under external light, there is such a problem that the display screen becomes dark.
In contrast to the above-described semi-transmission type reflection-mode liquid crystal display apparatus, a full reflection type liquid crystal display apparatus is arranged as follows. That is, while a forward lightening (illumination) apparatus is provided on a front surface of a liquid crystal display panel, a display screen of this liquid crystal display panel may be lightened by the forward lightening apparatus from the front surface under such a condition that a peripheral area around this full reflection type liquid crystal display apparatus becomes dark and thus, a display content of the display screen can be hardly observed. As a consequence, since such a large number of windows formed in the semi-transmission type liquid crystal display apparatus are no longer formed in a reflection plane of this full reflection type liquid crystal display apparatus, a light reflection efficiency at this reflection plane is not lowered. Even in such a case that the display screen of this full reflection-type liquid crystal display apparatus is illuminated by external light, the bright display screen may be obtained. In particular, this full reflection type liquid crystal display apparatus may be strongly expected to be employed in portable electronic appliances.
FIG. 1 is a sectional view for schematically indicating a structure of one conventional full (total) reflection type liquid crystal display apparatus 1. This full reflection type liquid crystal display apparatus 1 is arranged in such a manner that a forward lightening apparatus 3 is positioned on a front surface of a reflection type liquid crystal display panel 2. This reflection type liquid crystal display panel 2 is constituted by that a liquid crystal material 7 is sandwiched to be sealed between a board 4 and a glass board 6. A reflection plane 5 is formed on a surface of this board 4. In this liquid crystal display panel 2, such a constructual means is provided with each of pixels, by which incident light of this reflection type liquid crystal panel 2 may be reflected by the reflection plane 5 so as to be projected to a forward direction, and incident light may be absorbed not to be projected to the forward direction. The forward lightening apparatus 3 is constructed in such a manner that a light source unit 9 constituted by a cold cathode tube and the like is provided on a side surface of a transparent light conducting plate 8. It should be understood that light is represented by an arrow in this drawing, and will be similarly denoted in other drawings.
Thus, in accordance with such a full reflection type liquid crystal display apparatus 1, the forward lightening apparatus 3 is turned OFF in the case that a peripheral area of this full reflection type liquid crystal display apparatus 1 becomes bright. At this time, such external light is reflected on the reflection plane 5, and thereafter, this reflected external light is projected from the front surface of the full reflection type liquid crystal display apparatus 1, and then, this projected light is entered into eyes of a viewer. The external light corresponds to directly-entered sunlight, illumination (lightening) light, and the like, which pass through the forward lightening apparatus 3 and then, are entered into the liquid crystal display panel 2. On the other hand, when a peripheral area of this full reflection type liquid crystal display apparatus 1 becomes dark, the forward lightening apparatus 3 is turned ON. At this time, light projected from the light source unit 9 is entered from a side surface of the light conducting plate 8 into an internal portion of this light conducting plate 8. Then, while this entered light is fully-reflected between the front surface and the rear surface of the light conducting plate 8 in a repetition manner, this light is propagated within the light conducting plate 8. While the light is propagated inside the light conducting plate 8 in a half way, the propagation path of this light is bent by an optical pattern 10 which is provided on this light conducting plate 8. Then, such light which is entered into the rear surface of the light conducting plate 8 at a smaller incident angle then a critical angle of a total reflection of this light conducting plate 8 is projected from this rear surface of the light conducting plate 8 and then, is entered into the liquid crystal display panel 2. After this incident light is reflected from the reflection plane 5, the reflected light is projected from the front surface of the full reflection type liquid crystal display apparatus 1, and then, is entered into the eyes of the viewer.
While a concave/convex-shaped diffusion pattern is formed on the reflection plane 5, a directivity angle of reflection light may be expanded by this diffusion pattern, so that a visible range of a displayed image may be widened. Also, considering use conditions of such a full reflection type liquid crystal display apparatus 1, since there are many cases that both the external light and the viewers are positioned along a direction substantially perpendicular to the full reflection type liquid crystal display apparatus 1, the reflection characteristic of the reflection plane 5 is set in such a manner that the external light is diffused along such a direction approximated to a total reflection.
Also, both in the case that the display screen is viewed by using the external light and in the case that the display screen is viewed by turning ON the forward lightening apparatus 3, it is required that this display screen can be observed from the same direction. As a consequence, the forward projection light when the external light is used should be located substantially parallel to the forward projection light when the forward lightening apparatus 3 is employed. Moreover, in the conventional full reflection type liquid crystal display apparatus 1, since both the external light and the lightening light derived from the forward lightening apparatus 3 are reflected from the reflection planes having the common reflection characteristic (having same diffusion patterns) to the side of the viewer positioned forwardly, the lightening light of the forward lightening apparatus 3 is required to be entered into either the reflection plane or the liquid crystal display panel 2 from the same direction as that of the external light. As a consequence, the lightening light derived from the forward lightening apparatus 3 must be also projected along such a direction substantially perpendicular to the front surface of this full reflection type liquid crystal display apparatus 1. To this end, in the conventional forward lightening apparatus 3, while the very fine optical pattern 10 having the wedge shape is formed on the front surface of the light conducting plate 8, since the lightening light is totally reflected by this optical pattern 10, the light which is propagated through the light conducting plate 8 is converted into the light along the direction substantially perpendicular to the reflection plane 5. Then, after this light is matched to the direction which is located substantially parallel to the incident direction of the external light, the resultant light is projected from the rear surface to the liquid crystal display panel 2.
In the conventional liquid crystal display apparatus 1 with employment of the forward lightening apparatus 3, an air layer 11 is present between the forward lightening apparatus 3 and the liquid crystal panel 2. As indicated in FIG. 2, light which is projected from the rear surface of the forward lightening apparatus 3 is reflected on a boundary plane between this air layer 11 and the forward lightening apparatus 3, and also on another boundary plane between this air layer 11 and the liquid crystal display panel 2. Since this reflected light corresponds to such light which may not contribute the display operation of the liquid crystal display apparatus 1, this reflected light will be referred to as xe2x80x9cinvalid lightxe2x80x9d hereinafter. On the other hand, as explained in above, since the lighting light of the forward lightening apparatus 3 is entered from the direction perpendicular to the liquid crystal display panel 2 into the inside of this liquid crystal display panel 2, both the invalid light reflected on the boundary plane between the air layer 11 and the forward lightening apparatus 3, and the invalid light reflected on the boundary plane between the air layer 11 and the liquid crystal display panel 2 are projected along a direction substantially equal to the direction of the display-purpose light (namely, xe2x80x9cvalid lightxe2x80x9d for display operation) which is reflected on the reflection plane 5. As a consequence, both the display-purpose light and the invalid light are entered into the eyes of the viewer. Accordingly, there is such a problem that contrast of the display screen is lowered.
Also, the optical pattern 10 is provided on the front surface of the forward lightening apparatus 3. Moreover, since this optical pattern 10 is made in contact with air and therefore a difference in refractive indexes of the boundary planes is large, as indicated in FIG. 3, such light which is entered into a region 12 whose gradient is sharp (namely, stepped portion of boundary planes of optical pattern 10) may be totally reflected, may be largely refracted, and thus, may be readily scattered on a large area of the sharp gradient region 12 among such light which has been reflected on the reflection plane 5, and thereafter, is again entered into the internal portion of the forward lightening apparatus 3, and then, is projected from the front surface of the forward lightening apparatus 3. As a result, the transparent characteristic of the forward lightening apparatus 3 would be lowered (in other words, this condition is equivalent to such condition that diffusion plate is installed on surface of reflection type liquid crystal display apparatus).
The present invention has been made to solve the above-explained problems, and therefore, has an object to provide such a reflection type display apparatus in which a forward lightening apparatus is installed on a front surface of a reflection type display panel, while lowering of contrast of this reflection type display apparatus when the forward lightening apparatus is turned ON is avoided.
Another object of the present invention is to provide another reflection type display apparatus in which a forward lightening apparatus is installed on a front surface of a reflection type display panel, while diffusion of light caused by the forward lightening apparatus is suppressed and a transparent characteristic of the forward lightening apparatus is improved.
A further object of the present invention is to provide a method capable of manufacturing the above-described reflection type display apparatus, and also, to provide such an electronic appliance with employment of the above-explained reflection type display apparatus.
To achieve the above-described objects, a reflection type display apparatus, according to an aspect of the present invention, is featured by such a reflection type display apparatus comprising: a reflection type display panel having a reflection plane used to reflect thereon light entered from a forward direction; and a forward lightening apparatus arranged in front of the reflection type display panel; wherein: light which is entered from the forward lightening apparatus into the reflection type display panel is entered into the reflection type display panel along a direction different from a direction of external light entered into the reflection type display panel; and both the light which is derived from the forward lightening apparatus and is reflected on the reflection plane, and the external light which is reflected on the reflection plane are projected along the substantially same reflection direction.
In this case, as the reflection type display panel, a so-called xe2x80x9cliquid crystal display panelxe2x80x9d is typically known, but the present invention is not limited thereto. This liquid crystal display panel produces an image by utilizing a characteristic of liquid crystal, while the liquid crystal is sealed inside the liquid crystal display panel. Also, the external light implies such light which is entered from a peripheral portion such as direct sun light and illumination light except for the illumination light of the forward lightening apparatus. Normally, since a display screen is expected to be observed from a front surface thereof, external light is entered into the front surface of the reflection type display apparatus along a substantially vertical direction, and another external light reflected on the reflection plane is also projected along a direction perpendicular to the front surface. As a consequence, in such a case, the incident light of the forward lightening apparatus is obliquely entered with respect to the front surface of the reflection type display panel. However, the incident direction of the external light is not limited to the above-described incident direction. For example, the external light may be obliquely entered from the front surface of the reflection type display panel. Also, the direction for reflecting the external light may be made different from the regular reflection direction of the external light on the surface of each of the reflection type display panels in accordance with the following manner. That is, concave/convex patterns used to reflect the entered external light are made in an asymmetrical shape, the direction for reflecting the incident light derived from the forward lightening apparatus may be made different by adjusting the inclined planes of the concave/convex patterns used to reflect the incident light derived from the forward lightening apparatus. As a result, it is possible to avoid that the image can be hardly observed due to such light which is regularly reflected on the surface of the reflection type display panel.
In the reflection type display apparatus according to the present invention, both the light derived from the forward lightening apparatus, which is reflected on the reflection plane, and the external light which is reflected on the reflection plane are projected along the substantially same reflection directions. As a result, there is no change in the directions along which the display screen can be observed when the display screen is illuminated by employing the forward lightening apparatus and also when the display screen is illuminated by the external light without employing the forward lightening apparatus. Thus, easy operations of this reflection type display apparatus can be maintained. Moreover, in this reflection type display apparatus, since the light which is entered from the forward lightening apparatus into the reflection type display panel is entered into this reflection type display panel from such a direction different from the direction along which the external light is entered into the reflection type display panel, even when the light projected from the forward lightening apparatus is reflected on the surfaces, or the internal portions of the forward lightening apparatus and the reflection type display panel to become such invalid light which never contributes the display operation, this invalid light is not reflected along the same direction as that of the reflection light for the display purpose. As a consequence, in accordance with the reflection type display apparatus of the present invention, it is possible to avoid such a phenomenon that the contrast of the display screen is lowered by the reflection light of the forward lightening apparatus, so that the display screen can be easily observed.
The above-described reflection plane employed in an embodiment of the present invention, is subdivided into both a first region capable of reflecting thereon light which is obliquely entered from the forward lightening apparatus along the reflection direction, and a second region capable of reflecting thereon external light which is entered at a substantially right angle along the reflection direction. As a consequence, such reflection light which is entered along the different direction as that of the external light and is reflected from the reflection plane of the forward lightening apparatus can be projected along the substantially same reflection direction as that of the external light which is reflected on the reflection plane. Also, the second region may be arranged in such a manner that the second region is separated from the reflection plane of the reflection type display panel, and is arranged on a rear surface of the forward lightening apparatus constituted by a light source and a light conducting plate.
Also, the above-described reflection plane, according to another embodiment of the present invention, is featured by comprising: a first region on which a concave/convex pattern is formed, the concave/convex pattern reflecting thereon light which is obliquely entered from the forward lightening apparatus along the reflection direction; and a second region on which another concave/convex pattern is formed, the concave/convex pattern reflecting thereon external light which is entered at a substantially right angle along the reflection direction. As a consequence, such reflection light which is entered along the different direction as that of the external light and is reflected from the reflection plane of the forward lightening apparatus can be projected along the substantially same reflection direction as that of the external light which is reflected on the reflection plane.
Further, in another embodiment of the present invention in which the first region and the second region own the concave/convex patterns, a normal line stood on an averaged inclined surface of the concave/convex patterns formed on the first region is inclined from a direction perpendicular to the reflection plane toward a light source direction of the forward lightening apparatus. As a result, the incident light of the forward lightening apparatus which is obliquely entered from the light source side can be reflected along the forward direction. Also, the second region may be arranged in such a manner that the second region is separated from the reflection plane of the reflection type display panel, and is arranged on a rear surface of the forward lightening apparatus constituted by a light source and a light conducting plate.
Also, the above-explained reflection plane, according to another embodiment of the present invention, is featured by having substantially no such a region located in parallel to a front surface of said reflection type display panel. As a result, the external light entered along the forward direction can be hardly and again projected to the forward direction. As a consequence, while reducing such reflection light which is projected forwardly, and also can hardly observe the display content due to the reflections occurred except for the reflection plane, the reflection light of the external light may be reflected to another direction, so that the display screen can become bright.
Also, in accordance with a further embodiment of the present invention, at an arbitrary point on the reflection plane, a shape is modulated in such a manner that a normal line stood on an averaged inclined plane may be directed to a specific region located in front of the reflection plane. Both a reflection light luminance central axis of the entered external light, and a reflection light luminance central axis of the incident light for the forward lightening apparatus can be converged to a specific position located in front of the reflection type display panel. Thus, such an image which can be viewed at this specific position can become bright.
Also, the above-described forward lightening apparatus, according to a further embodiment of the present invention, is featured by comprising: a light source for projecting light; and a light conducting plate for confirming incident light in the own light conducting plate and for propagating the confined light through the own light conducting plate. As a result, such light may be projected from the rear surface of the light conducting plate along an oblique direction, while this light is entered at an angle smaller than a critical angle of a total reflection on the rear surface of the light conducting plate. As a consequence, since such a forward lightening apparatus is employed, the light of the forward lightening apparatus may be entered into the reflection type display panel from a direction different from the incident direction of the external light.
Furthermore, in the above-described embodiment, a thickness of an edge portion of the light conducting plate, which is located far from the light source, is made thinner than a thickness of a portion of the light conducting plate, which is located in the vicinity of the light source. In the light conducting plate having such a tapered shape, since the optical pattern used to project the light confined within the light conducting plate is no longer provided on this light conducting plate, the projected light is not diffused by this light conducting plate, and also the transparent characteristic of the forward lightening apparatus is not lowered.
Also, in such a case that both the front surface and the rear surface of the light conducting plate are made smooth, since the optical pattern used to project the light confined within the light conducting plate is no longer provided on this light conducting plate, the projected light is not diffused by this light conducting plate, and also the transparent characteristic of the forward lightening apparatus is not lowered.
Also, the above-described forward lightening apparatus, according to a further embodiment of the present invention, is featured by comprising a light source for projecting light; and a directivity improving unit for controlling directivity of light projected from said light source. Since the light projected from the light source is controlled by the directivity improving unit, the light may be obliquely entered into the front surface of the reflection type display panel. As a result, even when the light of the forward lightening apparatus is reflected on the front surface of the reflection type display panel, this reflected light is not reflected along the forward direction, but also, lowering of the contrast of the display screen caused by the reflective light can be avoided.
Also, in the reflection type display apparatus according to a further embodiment, a front surface of the light conducting plate is made smooth; and a pattern inclined in such a manner that a thickness of the light conducting plate on the side located far from the light source becomes thin is repeatedly formed on a rear surface of the light conducting plate. As a result, the light confined within the light conducting plate can be substantially unformly projected along the oblique direction from the rear surface of the light conducting plate by using the inclined pattern. Moreover, since the front surface of the light conducting plate is made smooth and also the inclined pattern can be hardly observed from the front surface, the transparent characteristic of the forward lightening apparatus can be hardly lowered.
Also, in the reflection type display apparatus according to a further embodiment, a rear surface of the light conducting plate is optically adhered to the reflection type display panel; and a low refractive index layer is formed between the light conducting plate and the reflection type display panel, the reflective index of the low refractive index layer being larger than a refractive index of air and smaller than a refractive index of the light conducting plate. As a result, the critical angle of the total reflection occurred on the rear surface of the conducting plate which is made in contact with the low refractive index layer may become larger than the critical angle of the total reflection occurred on the front surface of the light conducting plate which is made in contact with air. As a consequence, such light which is propagated through the light conducting plate is not projected from the front surface of the light conducting plate, but is projected from the rear surface of the light conducting plate to the reflection type display panel, so that the utilization efficiency of such light can be improved.
Also, in the case that the low refractive index layer is provided on the rear surface of the light conducting plate, there are some problems. That is, the light of the forward lightening apparatus is leaked in the vicinity of the light source to constitute loss, and the place locally becomes bright. In such a case, if a thickness of the light conducting plate becomes thin in accordance with a position where the light conducting plate reaches close to the light source within a region close to the light source then it is possible to prevent a leak of light in the vicinity of the light source.
Further, a manufacturing method of a reflection type display apparatus, according to another aspect of the present invention, is featured by such a manufacturing method in which under such a condition that resin supplied onto a board has not yet been hardened, or is softened, the resin is sandwiched between a stamper having an inverted pattern of a reflection plane and the board and then is depressed so as to transfer the inverted pattern of the stamper to the resin. As such a manufacturing method, there are one method for coating unhardened resin on a board and for sandwiching this resin between a stamper and the board. That is, after resin has been coated on a board by way of a spin coating manner, this coated resin is once hardened. Thereafter, this hardened resin is again heated to be softened, and then, this sifted resin is sandwiched between the stamper and the board. In accordance with this method, a predetermined reflection plane can be mass-produced in a high efficiency by way of the stamping method using the stamper. In particular, since the transfer time can be shortened in the latter method, this method may be properly applied to the mass production.
Further, a manufacturing method of a reflection type display apparatus, according to a further aspect of the present invention, is featured by such a manufacturing method in which ultraviolet hardening type resin is supplied onto a board; and under such a condition that the ultraviolet hardening type resin is sandwiched between a stamper having an inverted pattern of a reflection plane and the board, ultraviolet rays are irradiated to the ultraviolet hardening type resin so as to harden the ultraviolet hardening type resin, and then to transfer the inverted pattern of the stamper to the ultraviolet hardening type resin. In accordance with such a method, a predetermined reflection plane can be mass-produced in a high efficiency by way of the stamping method using the stamper. Moreover, the curing time after molding is no longer required by employing the ultraviolet hardening resin, the reflection plane can be formed in a higher efficiency.
Also, in the case that the reflection type display apparatus of the present invention is employed in a portable electronic appliance such as a portable telephone, a portable information terminal, a portable type computer (notebook type computer etc.), and a television, this reflection type display apparatus may be used as such a display unit capable of reducing power consumption, and capable of increasing contrast of a display screen thereof.
Furthermore, a light reflecting method, according to a still further aspect of the present invention, is featured by that in such a light reflecting method of a reflection type display apparatus equipped with a reflection type display panel having a reflection plane used to reflect thereon light entered from a forward direction, and a forward lightening apparatus arranged in front of the reflection type display panel, the light reflecting method is comprised of: a step for entering light which is entered from the forward lightening apparatus into the reflection type display panel into the reflection type display panel along a direction different from a direction of external light entered into the reflection type display panel; and a step for projecting both the light which is derived from the forward lightening apparatus and is reflected on the reflection plane, and the external light which is reflected on the reflection plane along the substantially same reflection direction.
It should be understood that the above-described structural elements of the present invention may be combined with each other, as being permitted as possible.